Molecular mechanical devices with a band gap change activated by an electric field for optical switching applications

ABSTRACT

Molecular systems are provided for electric field activated switches, such as optical switches. The molecular system has an electric field induced band gap change that occurs via one of the following mechanisms: (1) molecular conformation change; (2) change of extended conjugation via chemical bonding change to change the band gap; or (3) molecular folding or stretching. Nanometer-scale reversible optical switches are thus provided that can be assembled easily to make a variety of optical devices, including optical displays.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application ofSer. No. 09/823/195, filed Mar. 29, 2001 [PD-10010538-1], which in turnis a continuation-in-part application of Ser. No. 09/759,438, filed Jan.12, 2001 [PD-10003866-1], which in turn is a continuation-in-partapplication of Ser. No. 09/738,793, filed Dec. 14, 2000 [PD-10004762-1].

[0002] The present application is an improvement over the foregoingapplications in that it is directed to classes of molecules that provideswitching from one state to a different state, characterized by a changein the optical properties, including color, of the molecules. In thecase of color switching, the present invention turns ink or dye orpigment molecules into active opto-electronic devices that can beswitched by an external electric field.

TECHNICAL FIELD

[0003] The present invention relates generally to optical devices whosefunctional length scales are measured in nanometers, and, moreparticularly, to classes of molecules that provide optical switching.Optical devices both of micrometer and nanometer scale may beconstructed in accordance with the teachings herein.

BACKGROUND ART

[0004] The area of molecular electronics is in its infancy. To date,there have been two convincing demonstrations of molecules as electronicswitches published in the technical literature; see, C. P. Collier etal., Science, Vol. 285, pp. 391-394 (16 Jul. 1999) and C. P. Collier etal., Science, Vol. 289, pp. 1172-1175 (18 Aug. 2000), but there is agreat deal of speculation and interest within the scientific communitysurrounding this topic. In the published work, a molecule called arotaxane or a catenane was trapped between two metal electrodes andcaused to switch from an ON state to an OFF state by the application ofa positive bias across the molecule. The ON and OFF states differed inresistivity by about a factor of 100 and 5, respectively, for therotaxane and catenane.

[0005] The primary problem with the rotaxane was that it is anirreversible switch. It can only be toggled once. Thus, it can be usedin a programmable read-only memory (PROM), but not in a RAM-like (randomaccess memory) device nor in a re-configurable system, such as adefect-tolerant communications and logic network. In addition, therotaxane requires an oxidation and/or reduction reaction to occur beforethe switch can be toggled. This requires the expenditure of asignificant amount of energy to toggle the switch. In addition, thelarge and complex nature of rotaxanes and related compounds potentiallymakes the switching times of the molecules slow. The primary problemswith the catenanes are small ON-to-OFF ratio and a slow switching time.

[0006] Currently, there are a wide variety of known chromogenicmaterials that can provide optical switching in thin film form. Thesematerials and their applications have been reviewed recently by C. B.Greenberg, Thin Solid Films, Vol. 251, pp. 81-93 (1994) and R. J.Mortimer, Chemical Society Reviews, Vol. 26, pp. 147-156 (1997). Thesematerials are currently being studied for several applications,including active darkening of sunglasses, active darkening of windowsfor intelligent light and thermal management of buildings, and varioustypes of optical displays, such as heads-up displays on the inside ofwindshields of automobiles or airplanes and eye-glass displays.

[0007] Despite their long history of great promise, there are very fewphoton gating devices made from the existing classes of electrochromicmaterials. This is be-cause most of them require an oxidation-reductionreaction that involves the transport of ions, such as H+, Li⁺, or Na⁺through some type of liquid or solid electrolyte. Finding theappropriate electrolyte is a major problem, as is the slow speed of anydevice that requires transport of ions. Furthermore, such reactions areextremely sensitive to background contamination, such as oxygen or otherspecies, and thus degradation of the chromogenic electrodes is a majorlimitation.

[0008] In fact, for photonic switching applications such as a crossbarswitch router for a fiber optic communications network, the lack of asuitable chromogenic material has forced companies to use very differentapproaches: (a) transform the optical signal into an electronic signal,perform the switching operation, and then trans-form back to an opticalsignal before launching into a fiber (this is the most frequent solutionused today, but it is very inefficient and difficult for the electronicsto keep up with the data rates of the optical system); (b) use amoving-mirror array made by micro-electromechanical (MEM) processing toswitch optical data packets (this has the disadvantage that extremelyhigh tolerances are required for the device, which makes it veryexpensive); and (c) using ink jet technology to push bubbles into achamber to create a mirror to deflect an optical beam (this approachagain requires precision manufacturing and the switching time is slow).

[0009] Thus, what is needed is a molecular system that avoids chemicaloxidation and/or reduction, permits reasonably rapid switching from afirst state to a second, is reversible to permit real-time or video ratedisplay applications, and can be used in a variety of optical devices.

DISCLOSURE OF INVENTION

[0010] In accordance with the present invention, a molecular system isprovided for optical switching. The molecular system has an electricfield induced band gap change that occurs via one of the followingmechanisms:

[0011] (1) molecular conformation change or an isomerization;

[0012] (2) change of extended conjugation via chemical bonding change tochange the band gap; or

[0013] (3) molecular folding or stretching.

[0014] Changing of extended conjugation via chemical bonding change tochange the band gap may be accomplished in one of the following ways:

[0015] (a) charge separation or recombination accompanied by increasingor decreasing band localization; or

[0016] (b) change of extended conjugation via charge separation orre-combination and π-bond breaking or formation.

[0017] The present invention provides, e.g., optical switches that canbe assembled easily to make displays, electronic books, rewrittablemedia, electronic lenses, electrically-controlled tinting for windowsand mirrors, optical crossbar switches for fiber optic communications,and more. Such applications are discussed elsewhere, and are not germaneto the present invention, except to the extent that the optical switchof the present invention is employed in the construction of apparatus ofsuch applications.

[0018] The present invention introduces several new types of switchingmechanism: (1) an electric (E) field induced rotation of at least onerotatable section (rotor) of a molecule to change the band gap of themolecule; (2) E-field induced charge separation or re-combination of themolecule via chemical bonding change to change the band gap; (3) E-fieldinduced band gap change via molecule folding or stretching. Thesedevices are generically considered to be electric field devices, and areto be distinguished from earlier embodiments (described in theabove-mentioned related patent applications and patent) that aredirected to electrochemical devices.

[0019] The present invention also introduces the capability of usingmolecules for optical switches, in which the molecules change color whenchanging state. This property can be used for a wide variety of displaydevices or any other application enabled by a material that can changecolor or transform from transparent to colored.

[0020] Thus, the molecule is not oxidized nor reduced in the toggling ofthe switch. Also, the part of the molecule that moves is quite small, sothe switching time should be very fast. Also, the molecules are muchsimpler and thus easier and cheaper to make than the rotaxanes,catenanes, and related compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a schematic representation (perspective, transparentview) of a two color (e.g., black and white) display screen constructionfor use in accordance with the present invention;

[0022]FIG. 1a is a detail for a colorant layer element of the displayscreen depicted in FIG. 1;

[0023]FIG. 2 is a schematic representation (perspective, transparentview) of a full-color display screen construction for use in accordancewith the present invention;

[0024]FIG. 3 is a schematic representation of a scan addressingembodiment of a two-color display screen construction for use inaccordance with the present invention;

[0025]FIG. 4 is a schematic model depicting an E-field-induced band gapchange via molecular conformation change (rotor/stator type of model);

[0026]FIG. 5a depicts a molecule comprising a middle rotor portion witha dipole and two end stator portions;

[0027]FIG. 5b is a schematic representation (perspective) of themolecule depicted in FIG. 5a, illustrating the planar state, with therotor and stators all co-planar;

[0028]FIG. 5c is also a schematic representation (perspective),illustrating the rotated state, with the rotor rotated 90° with respectto the stators;

[0029]FIG. 6a is a schematic model depicting an E-field-induced band gapchange caused by the change of extended conjugation via chargeseparation or recombination accompanied by increasing or decreasing bandlocalization;

[0030]FIG. 6b is a schematic model depicting an E-field-induced band gapchange caused by change of extended conjugation via charge separation orrecombination and 1-bond breaking or formation; and

[0031]FIG. 7 is a schematic model depicting an E-field-induced band gapchange via molecular folding or stretching.

BEST MODES FOR CARRYING OUT THE INVENTION

[0032] A. Definitions

[0033] The term “self-assembled” as used herein refers to a system thatnaturally adopts some geometric pattern because of the identity of thecomponents of the system; the system achieves at least a local minimumin its energy by adopting this configuration.

[0034] The term “singly configurable” means that a switch can change itsstate only once via an irreversible process such as an oxidation orreduction reaction; such a switch can be the basis of a programmableread-only memory (PROM), for example.

[0035] The term “reconfigurable” means that a switch can change itsstate multiple times via a reversible process such as an oxidation orreduction; in other words, the switch can be opened and closed multipletimes, such as the memory bits in a random access memory (RAM) or acolor pixel in a display.

[0036] The term “bi-stable” as applied to a molecule means a moleculehaving two relatively low energy states (local minima) separated by anenergy (or activation) barrier. The molecule may be either irreversiblyswitched from one state to the other (singly configurable) or reversiblyswitched from one state to the other (reconfigurable). The term“multi-stable” refers to a molecule with more than two such low energystates, or local minima.

[0037] Micron-scale dimensions refers to dimensions that range from 1micrometer to a few micrometers in size.

[0038] Sub-micron scale dimensions refers to dimensions that range from1 micrometer down to 0.05 micrometers.

[0039] Nanometer scale dimensions refers to dimensions that range from0.1 nanometers to 50 nanometers (0.05 micrometers).

[0040] Micron-scale and submicron-scale wires refers to rod orribbon-shaped conductors or semiconductors with widths or diametershaving the dimensions of 0.05 to 10 micrometers, heights that can rangefrom a few tens of nanometers to a micrometer, and lengths of severalmicrometers and longer.

[0041] “HOMO” is the common chemical acronym for “highest occupiedmolecular orbital”, while “LUMO” is the common chemical acronym for“lowest unoccupied molecular orbital”. HOMOs and LUMOs are responsiblefor electronic conduction in molecules and the energy difference betweenthe HOMO and LUMO and other energetically nearby molecular orbitals isresponsible for the color of the molecule.

[0042] An optical switch, in the context of the present invention,involves changes in the electromagnetic properties of the molecules,both within and outside that detectable by the human eye, e.g., rangingfrom the far infra-red (IR) to deep ultraviolet (UV). Optical switchingincludes changes in properties such as absorption, reflection,refraction, diffraction, and diffuse scattering of electromagneticradiation.

[0043] The term “transparency” is defined within the visible spectrum tomean that optically, light passing through the colorant is not impededor altered except in the region in which the colorant spectrallyabsorbs. For example, if the molecular colorant does not absorb in thevisible spectrum, then the colorant will appear to have water cleartransparency.

[0044] The term “omni-ambient illumination viewability” is definedherein as the viewability under any ambient illumination condition towhich the eye is responsive.

[0045] B. Optical Switches

[0046] Optical switches are described in greater detail in co-pendingU.S. application Ser. No. ______, filed on ______ [PD-10005747-1]. Ageneric example taken from that application is depicted herein in FIG.1, wherein a display screen 100 is shown that incorporates at least onecolorant layer 101. The colorant layer 101 comprises a pixel array usingelectrical field switchable, reconfigurable, dye or pigment molecules ofthe present invention, described in greater detail below and genericallyreferred to as a “molecular colorant”. Each dye or pigment molecule isfield switchable either between an image color (e.g., black) andtransparent or between two different colors (e.g., red and green).

[0047] Referring briefly to FIG. 1a, the colorant layer 101 is anaddressable pixel array formed of bi-stable molecules arrayed such thata selected set of molecules correlates to one pixel. The colorant layer101 is a thin layer coated on a background substrate 103 having thedisplay's intended background color (e.g., white). The substrate 103 maycomprise, for example, a high dielectric pigment (e.g., titania) in apolymer binder that provides good white color and opacity while alsominimizing the voltage drop across the layer. The stratified combinationof colorant layer 101 and substrate 103 thus is fully analogous to alayer of ink on paper. In a blank mode, or erased state, each moleculeis switched to its transparent orientation; the “layer of ink” isinvisible. The background (e.g., white pixels) shows through in thosepixel areas where the colorant layer 101 molecules are switched to thetransparent orientation. A transparent view-through layer 105, such asof a clear plastic or glass, is provided superjacent to thecolorant-background sandwich to provide appropriate protection. Theview-through layer 105 has a transparent electrode array 107 for pixelcolumn or row activation mounted thereto and positioned superjacently tothe colorant layer 101. The background substrate 103 has a complementaryelectrode array 109 for pixel row or column activation mounted thereto(it will be recognized by those skilled in the art that a specificimplementation of the stratification of the electrode arrays 107, 109for matrix addressing and field writing of the individual pixels mayvary in accordance with conventional electrical engineering practices).Optionally, the pixels are sandwiched by employing thin film transistor(TFT) driver technology as would be known in the art.

[0048] The present display 100 is capable of the same contrast and coloras hard copy print. A molecular colorant is ideal because its size andmass are infinitesimally small, allowing resolution and colorantswitching times that are limited only by the field writing electrodesand circuitry. Like ink, the colorant layer 101 may develop adequatedensity in a sub-micron to micron thin layer, potentially lowering thefield voltage required to switch the colorant between logic states andthus allowing the use of inexpensive drive circuitry.

[0049] Suitable reconfigurable bi-stable molecules for use in suchdisplays are disclosed below and claimed herein. In the main, thesemolecules have optical properties (e.g., color) that are determined bythe extent of their π orbital electron conjugation. The opticalproperties, including color or transparency, of the molecule change withfield polarity applied across the molecule and remains chromaticallystable in the absence of an applied electric field. By disrupting thecontinuity of conjugation across a molecule, the molecule may be changedfrom one optical state to another, e.g., colored to transparent.Electric dipoles may be designed into the colorant that can physicallycause this disruption by rotating or otherwise distorting certainsegments of the dye or pigment molecule relative to other segments, whenan external electric field is applied or changed.

[0050] The colorant layer 101 is a homogeneous layer of molecules whichare preferably colored (e.g., black, cyan, magenta, or yellow) in amore-conjugated orientation and transparent in a less-conjugatedorientation. By making the abutting back-ground substrate 103 white, thecolorant layer 101 may thereby produce high contrast black and white,and colored images. The colorant layer 101 may comprise a single fieldswitchable dye or pigment or may comprise a mixture of differentswitchable dyes or pigments that collectively produce a composite color(e.g., black). By using a molecular colorant, the resolution of theproduced image is limited only by the electric field resolution producedby the electrode array 107, 109. The molecular colorant additionally hasvirtually instantaneous switching speed, beneficial to the needs of fastscanning (as described with respect to FIG. 3 hereinafter). In certaincases, the molecular colorant may be contained in a polymeric layer.Polymers for producing such coatings are well-known, and include, forexample, acrylates, urethanes, and the like. Alternatively, the colorantlayer 101 may be self-assembled.

[0051] In one embodiment, the colorant layer 101 is offered as asubstitute for matrix-addressed liquid crystal flat panel displays. Asis well-known for such displays, each pixel is addressed through rowsand columns of fixed-position electrode arrays, e.g., 107, 109. Thefixed-position electrode arrays 107, 109 consist of conventionalcrossbar electrodes 111, 113 that sandwich the colorant layer 101 toform an overlapping grid (matrix) of pixels, each pixel being addressedat the point of electrode overlap. The crossbar electrodes 111, 113comprise parallel, spaced electrode lines arranged in electrode rows andcolumns, where the row and column electrodes are separated on opposingsides of the colorant layer 101. Preferably, a first set of transparentcrossbar electrodes 107 (201, 203 in FIG. 2 described in detailhereinafter) is formed by thin film deposition of indium tin oxide (ITO)on a transparent substrate (e.g., glass). These row addressable pixelcrossbar electrodes 107 are formed in the ITO layer using conventionalthin film patterning and etching techniques. The colorant layer 101 andbackground substrate 103 are sequentially coated over or mounted to thetransparent electrode layer, using conventional thin film techniques(e.g., vapor deposition) or thick film techniques (e.g., silkscreen,spin cast, or the like). Additional coating techniques includeLangmuir-Blodgett deposition and self-assembled mono-layers. Columnaddressable pixel crossbar electrodes 109 (202, 204 in FIG. 2) arepreferably constructed in like manner to the row electrodes 107. Thecolumn addressable pixel crossbar electrodes 109 may optionally beconstructed on a separate substrate that is subsequently adhered to thewhite coating using conventional techniques.

[0052] This display 100, 200 provides print-on-paper-like contrast,color, viewing angle, and omni-ambient illumination viewability byelimination of the polarization layers required for known liquid crystalcolorants. Using the described-display also allows a significantreduction in power drain. Whereas liquid crystals re-quire a holdingfield even for a static image, the present molecules of the colorantlayer 101 can be modal in the absence of a field when bi-stablemolecules are used. Thus, the present bi-stable colorant layer 101 onlyrequires a field when a pixel is changed and only for that pixel. Thepower and image quality improvements will pro-vide significant benefitin battery life and display readability, under a wider range of viewingand illumination conditions for appliances (e.g., wristwatches,calculators, cell phones, or other mobile electronic applications)television monitors and computer displays. Furthermore, the colorantlayer may comprise a mosaic of colored pixels using an array ofbi-stable color molecules of various colors for lower resolution colordisplays.

[0053] Since each colorant molecule in colorant layer 101 is transparentout-side of the colorant absorption band, then multiple colorant layersmay be superimposed and separately addressed to produce higherresolution color displays than currently available. FIG. 2 is aschematic illustration of this second embodiment. A high resolution,full color, matrix addressable, display screen 200 comprises alternatinglayers of transparent electrodes—row electrodes 201, 203 and columnelectrodes 202 and 204—and a plurality of colorant layers 205, 207, 209,each having a different color molecule array. Since each pixel in eachcolorant layer may be colored or trans-parent, the color of a givenpixel may be made from any one or a combination of the color layers(e.g., cyan, magenta, yellow, black) at the full address resolution ofthe display. When all colorant layers 205, 207, 209 for a pixel are madetransparent, then the pixel shows the background substrate 103 (e.g.,white). Such a display offers the benefit of three or more timesresolution over present matrix LCD devices having the same pixel densitybut that rely on single layer mosaic color. Details of the fabricationof the display are set forth in the above-mentioned co-pendingapplication.

[0054] The color to be set for each pixel is addressed by applying avoltage across the electrodes directly adjacent to the selected colorlayer. For example, assuming yellow is the uppermost colorant layer 205,magenta is the next colorant layer 207, and cyan is the third colorantlayer 209, then pixels in the yellow layer are addressed through rowelectrodes 201 and column electrodes 202, magenta through columnelectrodes 202 and row electrodes 203, and cyan through row electrodes203 and column electrodes 204. This simple common electrode addressingscheme is made possible because each colorant molecule is color stablein the absence of an applied electric field.

[0055]FIG. 3 depicts a third embodiment, which employs scan-addressingrather than matrix-addressing. Matrix address displays are presentlylimited in resolution by the number of address lines and spaces that maybe patterned over the relatively large two-dimensional surface of adisplay, each line connecting pixel row or column to the outer edge ofthe display area. In this third embodiment, the bi-stable molecularcolorant layer 101 and background substrate 103 layer construction iscombined with a scanning electrode array printhead to provide a scanningelectrode display apparatus 300 having the same readability benefits asthe first two embodiments described above, with the addition ofcommercial publishing resolution. Scanning electrode arrays and driveelectronics are common to electrostatic printers and their constructionsand interfaces are well-known. Basically, remembering that the bi-stablemolecular switch does not require a holding field, the scanningelectrode array display apparatus 300 changes a displayed image byprinting a pixel row at a time. The scanning electrode array displayapparatus 300 thus provides far greater resolution by virtue of theability to alternate odd and even electrode address lines along opposingsides of the array, to include multiple address layers with pass-througharray connections and to stagger multiple arrays that proportionatelysuperimpose during a scan. The colorant layer 101 may again be patternedwith a color mosaic to produce an exceptionally high resolution scanningcolor display.

[0056] More specifically, the third embodiment as shown in FIG. 3comprises a display screen 302, a scanned electrode array 304, and arraytranslation mechanism 301 to accurately move the electrode array acrossthe surface of the screen. The display screen 302 again comprises abackground substrate 103, a transparent view-through layer 105, and atleast one bi-stable molecule colorant layer 101. The colorant layer 101may include a homogeneous monochrome colorant (e.g., black) or colormosaic, as described herein above. The scanned electrode array 304comprises a linear array or equivalent staggered array of electrodes incontact or near contact with the background substrate 103. A staggeredarray of electrodes may be used, for example, to minimize fieldcrosstalk between otherwise adjacent electrodes and to increase displayresolution.

[0057] In operation, each electrode is sized, positioned, andelectrically ad-dressed to provide an appropriate electric field,represented by the arrow labeled “E”, across the colorant layer 101 at agiven pixel location along a pixel column. The field E may be orientedperpendicular to the plane of the colorant layer 101 or parallel to it,depending on the color switching axis of the colorant molecules. Aperpendicular field may be produced by placing a common electrode (e.g.,an ITO layer) on the opposing coating side to the electrode array. Theelectrode array may also be constructed to emit fringe fields; aparallel fringe field may be produced by placing a common electrodeadjacent and parallel to the array. A perpendicular fringe field may beproduced by placing symmetrically spaced parallel common electrodesabout the electrode array(s). The voltage is adjusted so that thedominant field line formed directly beneath the array 304 issufficiently strong to switch the addressed colorant molecule(s) anddivided return lines are not. Additional information regarding alternateembodiments and scanning mechanisms are discussed in the above-mentionedco-pending application.

[0058] C. Present Invention

[0059] In accordance with the present invention, molecules evidencingone of several new types of switching are provided for the colorantlayer 101. That is to say, the present invention introduces several newtypes of switching mechanisms that distinguish it from the prior art:

[0060] (1) an electric field (“E-field”) induced rotation of at leastone rotatable section (rotor) or a molecule to change the band gap ofthe molecule;

[0061] (2) E-field induced charge separation or recombination of themolecule via chemical bonding change to change the band gap; and

[0062] (3) E-field induced band gap change via molecular folding orstretching. Thus, the color switching is the result of an E-fieldinduced intramolecular change rather than a diffusion oroxidation/reduction reaction, in contrast to prior art approaches. Also,the part of the molecule that moves is quite small, so the switchingtime is expected to be quite fast. Also, the molecules are much simplerand thus easier and cheaper to make than the rotaxanes, catenanes, andrelated compounds.

[0063] The following are examples of model molecules with a briefdescription of their function:

[0064] (1) E-field induced band gap change via molecular conformationchange (rotor/stator type of model)— FIGS. 4 and 5a-5 c;

[0065] (2a) E-field-induced band gap change caused by the change ofextended conjugation via charge separation or recombination accompaniedby increasing or decreasing band localization —FIG. 6a;

[0066] (2b) E-field-induced band gap change caused by change of extendedconjugation via charge separation or recombination and π-bond breakingor formation—FIG. 6b; and

[0067] (3) E-field-induced band gap change via molecule folding orstretching—FIG. 7.

[0068] Each model, with supporting examples, is discussed below.However, the examples given are not to be considered limiting theinvention to the specific molecular systems illustrated, but rathermerely exemplary of the above switching mechanisms.

[0069] Model (1): E-Field-Induced Band Gap Change Via MolecularConformation Change (Rotor/Stator Type of Model):

[0070]FIG. 4 is a schematic depiction of one embodiment of this model,which involves an E-field-induced band gap change via molecularconformation change (rotor/stator type of model). As shown in FIG. 4,the molecule 430 comprises a rotor portion 432 and a stator portion 434.The rotor portion 432 rotates with an applied electric field. In onestate, depicted on the left side of the drawing, there is an extendedconjugation through the entire molecule, resulting in a relativelysmaller band gap and thereby longer wavelength (red-shifted)photo-absorption. In the other state, following rotation of the rotor,depicted on the right side of the drawing, the extended conjugation isdestroyed, resulting in a relatively larger band gap and thereby shorterwavelength (blue-shifted) photo-absorption. FIGS. 5a-5 c depict analternate, and preferred, embodiment of this Model 1; these latterFigures are discussed in connection with Examples 1 and 2 of this Model1 below.

[0071] The following requirements must be met in this model:

[0072] (a) The molecule must have at least one rotor segment and atleast one stator segment;

[0073] (b) In one state of the molecule, there should be delocalizedHOMOs and/or LUMOs (π-states and/or non-bonding orbitals) that extendover a large portion of the molecule (rotor(s) and stator(s)), whereasin the other state, the orbitals are localized on the rotor(s) andstator(s), and other segments;

[0074] (c) The connecting unit between rotor and stator can be a singleσ-bond or at least one atom with (1) non-bonding electrons (p or otherelectrons), or (2) π-electrons, or (3) π-electrons and non-bondingelectron(s);

[0075] (d) The non-bonding electrons, or π-electrons, or π-electrons andnon-bonding electron(s) of the rotor(s) and stator(s) can be localizedor de-localized depending on the conformation of the molecule, while therotor rotates when activated by an E-field;

[0076] (e) The conformation(s) of the molecule can be E-field dependentor bi-stable;

[0077] (f) The bi-stable state(s) can be achieved by intra- orinter-molecular forces such as hydrogen bonding, Coulomb force, van derWaals force, metal ion complex or dipole inter-stabilization; and

[0078] (g) The band gap of the molecule will change depending on thedegree of non-bonding electron, or π-electron, or π-electron andnon-bonding electron de-localization of the molecule. This will controlthe optical properties (e.g., color and/or index of refraction, etc.) ofthe molecule.

[0079] Following are two examples of this model (Examples 1 and 2):

[0080] The novel bi-modal molecules of the present invention are activeoptical devices that can be switched with an external electric field.Preferably, the colorant molecules are bi-stable. The general idea is todesign into the molecules a rotatable middle segment (rotor) 432 thathas a large dipole moment (see Examples 1 and 2) and that links twoother portions of the molecule 430 that are immobilized (stators) 434.Under the influence of an applied electric field, the vector dipolemoment of the rotor 432 will attempt to align parallel to the directionof the external field. However, the molecule 430 is designed such thatthere are inter- and/or intra-molecular forces, such as hydrogen bondingor dipole-dipole interactions as well as steric repulsions, thatstabilize the rotor 432 in particular orientations with respect to thestators 434. Thus, a large electric field is required to cause the rotor432 to unlatch from its initial orientation and rotate with respect tothe stators 434.

[0081] Once switched into a particular orientation, the molecule 430will re-main in that orientation until it is switched to a differentorientation, or reconfigured. However, a key component of the moleculedesign is that there is a steric repulsion or hindrance that willprevent the rotor 432 from rotating through a complete 180 degree halfcycle. Instead, the rotation is halted by the steric interaction ofbulky groups on the rotor 432 and stators 434 at an opticallysignificant angle of typically between 10° and 170° from the initialorientation. For the purposes of illustration, this angle is shown as90° in the present application. Furthermore, this switching orientationmay be stabilized by a different set of inter- and/or intra-molecularhydrogen bonds or dipole interactions, and is thus latched in place evenafter the applied field is turned off. For bi- or multi-stable colorantmolecules, this ability to latch the rotor 432 between two statesseparated by an optically significant rotation from the stators iscrucial.

[0082] The foregoing strategy may be generalized to design colorantmolecules to provide several switching steps so as to allow multiplestates (more than two) to produce a multi-state (e.g., multi-color)system. Such molecules permit the optical proper ties of the colorantlayer to be tuned continuously with a decreasing or increasing electricfield, or changed abruptly from one state to another by applying apulsed field.

[0083] Further, the colorant molecules may be designed to include thecase of no, or low, activation barrier for fast but volatile switching.In this latter situation, bi-stability is not required, and the moleculeis switched into one state by the electric field and relaxes back intoits original state upon removal of the field (“bi-modal”). In effect,these forms of the bi-modal colorant molecules are “self-erasing”. Incontrast, with bi-stable colorant molecules, the colorant moleculeremains latched in its state upon removal of the field (non-volatileswitch), and the presence of the activation barrier in that caserequires application of an opposite field to switch the molecule back toits previous state.

[0084] When the rotor 432 and stators 434 are all co-planar, themolecule is referred to as “more-conjugated”. Thus, the non-bondingelectrons, or π-electrons, or π-electrons and non-bonding electrons ofthe colorant molecule, through its highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital (LUMO), are delocalizedover a large portion of the molecule 430. This is referred to as a “ared-shifted state” for the molecule, or “optical state I”. In the casewhere the rotor 432 is rotated out of conjugation by approximately 90°with respect to the stators 434, the conjugation of the molecule 430 isbroken and the HOMO and LUMO are localized over smaller portions of themolecule, referred to as “less-conjugated”. This is a “blue-shiftedstate” of the molecule 430, or “optical state II”. Thus, the colorantmolecule 430 is reversibly switchable between two different opticalstates.

[0085] It will be appreciated by those skilled in the art that in theideal case, when the rotor 432 and stators 434 are completely coplanar,then the molecule is fully conjugated, and when the rotor 432 is rotatedat an angle of 90° with respect to the stators 434, then the molecule isnon-conjugated. However, due to thermal fluctuations, these ideal statesare not fully realized, and the molecule is thus referred to as being“more-conjugated” in the former case and “less-conjugated” in the lattercase. Further, the terms “red-shifted” and “blue-shifted” are not meantto convey any relationship to hue, but rather the direction in theelectromagnetic energy spectrum of the energy shift of the gap betweenthe HOMO and LUMO states.

[0086] Examples 1 and 2 show two different orientations for switchingthe molecules. Example 1a below depicts a first generic molecularexample for this Model 1.

Con₁Con₂SB SA A⁻D⁺ Connecting Group Connecting Group Stator B Stator AAcceptor (Electron withdrawing group) Donor (Electron donating group)

EXAMPLE 1a

[0087] where:

[0088] The letter A⁻ represents an Acceptor group; it is anelectron-withdrawing group. It may be one of the following: hydrogen,carboxylic acid or its derivatives, sulfuric acid or its derivatives,phosphoric acid or its derivatives, nitro, nitrile, hetero atoms (e.g.,N, O, S, P, F, Cl, Br), or functional groups with at least one ofabove-mentioned hetero atoms (e.g., OH, SH, NH, etc.), hydrocarbons(either saturated or unsaturated) or substituted hydrocarbons.

[0089] The letter D⁺ represents a Donor group; it is anelectron-donating group. It may be one of following: hydrogen, amine,OH, SH, ether, hydrocarbon (either saturated or unsaturated), orsubstituted hydrocarbon or functional group with at least one of heteroatom (e.g., B, Si, I, N, O, S, P). The donor is differentiated from theacceptor by that fact that it is less electronegative, or moreelectropositive, than the acceptor group on the molecule.

[0090] The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

[0091] The letters SA and SB are used here to designate Stator A andStator B. They may be a hydrocarbon (either unsaturated or saturated) orsubstituted hydrocarbon. Typically, these hydrocarbon units containconjugated rings that contribute to the extended conjugation of themolecule when it is in a planar state (red shifted state). In thosestator units, they may contain the bridging group G_(n) and/or thespacing group R_(n). The bridging group (e.g., acetylene, ethylene,amide, imide, imine, azo, etc.) is typically used to connect the statorto the rotor or to connect two or more conjugated rings to achieve adesired chromophore. The connector may alternately comprise a singleatom bridge, such as an ether bridge with an oxygen atom, or a directsigma bond between the rotor and stator. The spacing groups (e.g.,phenyl, isopropyl or tert-butyl, etc.) are used to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing space for each rotor to rotate over thede-sired range of motion.

[0092] Example 1b below is a real molecular example of Model 1. InExample 1b, the rotation axis of the rotor is designed to be nearlyperpendicular to the net current-carrying axis of the molecules, whereasin Example 2, the rotation axis is parallel to the orientation axis ofthe molecule. These designs allow different geometries of molecularfilms and electrodes to be used, depending on the desired results.

EXAMPLE 1b

[0093] where:

[0094] The letter A⁻ is an Acceptor group; it is an electron-withdrawinggroup. It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

[0095] The letter D⁺ represents a Donor group; it is anelectron-donating group. It may be one of following: hydrogen, amine,OH, SH, ether, hydrocarbon (either saturated or unsaturated), orsubstituted hydrocarbon or functional group with at least one of heteroatom (e.g., B, Si, I, N, O, S, P). The donor is differentiated from theacceptor by that fact that it is less electronegative, or moreelectropositive, than the acceptor group on the molecule.

[0096] The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g. metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

[0097] Letters R₁, R₂, R₃ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0098] Letters G₁, G₂, G₃, and G₄ are bridging groups. The function ofthese bridging groups is to connect the stator and rotor or to connecttwo or more conjugated rings to achieve a desired chromophore. They maybe any one of the following: hetero atoms (e.g., N, O, S, P, etc.) orfunctional groups with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbons (either saturated or unsaturated)or substituted hydrocarbons. The connector may alternately comprise asingle atom bridge such as an ether bridge with an oxygen atom, or adirect sigma bond between the rotor and stator.

[0099] In Example 1b above, the vertical dotted lines represent othermolecules or solid substrates. The direction of the switching field isperpendicular to the vertical dotted lines. Such a configuration isemployed for electrical switching; for optical switching, the linkingmoieties may be eliminated, and the molecule may be simply placedbetween the two electrodes. They may also be simply used to link onemolecule to another molecule or a molecule to an organic or inorganicsolid substrate.

[0100] Referring to FIG. 5a, the molecule shown above (Example 1b) hasbeen designed with the internal rotor 432 perpendicular to theorientation axis of the entire molecule 430. In this case, the externalfield is applied along the orientation axis of the molecule 430 aspictured—the electrodes (vertical dotted lines) are orientedperpendicular to the plane of the paper and perpendicular to theorientation axis of the molecule 430. Application of an electric fieldoriented from left to right in the diagrams will cause the rotor 432 aspictured in the upper diagram to rotate to the position shown on thelower right diagram, and vice versa. In this case, the rotor 432 aspictured in the lower right diagram is not coplanar with the rest of themolecule, so this is the blue-shifted optical state of the molecule,whereas the rotor is coplanar with the rest of the molecule on the upperdiagram, so this is the red-shifted optical state of the molecule. Thestructure shown in the lower left diagram depicts the transition stateof rotation between the upper diagram (co-planar, conjugated) and thelower right diagram (central portion rotated, non-conjugated).

[0101] The molecule depicted in Example 1b is chromatically transparentor blue-shifted. In the conjugated state, the molecule is colored or isred-shifted.

[0102] For the molecules in Example 1b, a single monolayer molecularfilm is grown, for example using Langmuir-Blodgett techniques orself-assembled monolayers, such that the orientation axis of themolecules is perpendicular to the plane of the electrodes used to switchthe molecules. Electrodes may be deposited in the manner described byCollier et al, supra, or methods described in the above-referencedpatent applications and issued patent. Alternate thicker film depositiontechniques include vapor phase deposition, contact or ink-jet printing,or silk screening.

[0103] Example 2a below depicts a second generic molecular example forthis Model 1.

Con₁Con₂SB SA A⁻D⁺ Connecting Group Connecting Group Stator B Stator AAcceptor (Electron withdrawing group) Donor (Electron donating group)

EXAMPLE 2a

[0104] where:

[0105] The letter A⁻ is an Acceptor group; it is an electron-withdrawinggroup. It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

[0106] The letter D⁺ represents a Donor group; it is anelectron-donating group. It may be one of following: hydrogen, amine,OH, SH, ether, hydrocarbon (either saturated or unsaturated), orsubstituted hydrocarbon or functional group with at least one of heteroatom (e.g., B, Si, I, N, O, S, P). The donor is differentiated from theacceptor by that fact that it is less electronegative, or moreelectropositive, than the acceptor group on the molecule.

[0107] The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

[0108] The letters SA and SB are used here to designate Stator A andStator B. They can be a hydrocarbon (either unsaturated or saturated) orsubstituted hydrocarbon. Typically, these hydrocarbon units containconjugated rings that contribute to the extended conjugation of themolecule when it is in a planar state (red shifted state). In thosestator units, they may contain bridging groups G_(n) and/or spacinggroups R_(n). A bridging group is typically used to connect the statorand rotor or to connect two or more conjugated rings to achieve adesired chromophore The connector may alternately comprise a single atombridge, such as an ether bridge with an oxygen atom, or a direct sigmabond between the rotor and stator. A spacing group provides anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor.

[0109] Example 2b below is another real molecular example of Model 1.

EXAMPLE 2b

[0110] where:

[0111] The letter A⁻ is an Acceptor group; it is an electron-withdrawinggroup. It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

[0112] The letter D⁺ represents a Donor group; it is anelectron-donating group. It may be one of following: hydrogen, amine,OH, SH, ether, hydrocarbon (either saturated or unsaturated), orsubstituted hydrocarbon or functional group with at least one of heteroatom (e.g., B, Si, I, N, O, S, P). The donor is differentiated from theacceptor by that fact that it is less electronegative, or moreelectropositive, than the acceptor group on the molecule.

[0113] The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

[0114] The letters R₁, R₂ and R₃ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0115] The letters G₁, G₂, G₃, G₄, G₅, G₆, G₇, and G₈ are bridginggroups. The function of these bridging groups is to connect the statorand rotor or to connect two or more conjugated rings to achieve adesired chromophore. They may be any one of the following: hetero atoms(e.g., C, N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH or NHNH, etc.), hydrocarbons(either saturated or unsaturated) or substituted hydrocarbons. Theconnector may alternately comprise a single atom bridge such as an etherbridge with an oxygen atom, or a direct sigma bond between the rotor andstator.

[0116] The letters J₁ and J₂ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is to provide an appropriate functional effect (e.g. bothinductive effect and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO /LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecular conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g. hydrogen bonding, Coulomb interaction, van der Waals forces) or toprovide bi- or multiple-stability of molecular orientations. They may beany one of the following: hydrogen, hetero atoms (e.g., N, O, S, P, B,F, Cl, Br, and I), functional groups with at least one ofabove-mentioned hetero atoms, hydrocarbons (either saturated orunsaturated) or substituted hydrocarbons.

[0117] The molecule shown above (Example 2b) has been designed with theinternal rotor parallel to the orientation axis of the entire molecule.In this case, the external field is applied perpendicular to themolecular axis—the electrodes are oriented parallel to the long axis ofthe molecule and can be either nominally perpendicular or parallel tothe plane of the above model structures. For example, application of anelectric field to the upper molecule shown above where the field linesare perpendicular to the molecular axis and pointing upward will causethe rotor as pictured in that diagram to rotate to approximately 90degrees and appear edge on, as shown in the lower molecular diagramabove, and vice versa. In this case, the rotor as pictured in the lowerdiagram is not coplanar with the rest of the molecule, so this is theblue-shifted optical state of the molecule, or optical state II, whereasthe rotor is coplanar with the rest of the molecule on the upperdiagram, so this is the red-shifted optical state of the molecule, oroptical state I. The letters N, H, and O retain their usual meaning.).

[0118]FIG. 5a depicts molecules similar to those of Examples 1b and 2b,but simpler, comprising a middle rotor portion 432 and two end statorportions 434. As in Examples 1b and 2b, the rotor portion 432 comprisesa benzene ring that is provided with substituents that render the rotorwith a dipole. The two stator portions 434 are each covalently bonded tothe benzene ring through an azo linkage, and both portions comprise anaromatic ring.

[0119]FIG. 5b is a schematic representation (perspective), illustratingthe planar state, with the rotor 432 and stators 434 all co-planar. Inthe planar state, the molecule 430 is fully conjugated, evidences color(first spectral or optical state), and is comparatively moreelectrically conductive. The conjugation of the rings is illustrated bythe π-orbital clouds 500 a, 500 b above and below, respectively, theplane of the molecule 430.

[0120]FIG. 5c is also a schematic representation (perspective),illustrating the rotated state, with the rotor 432 rotated 90° withrespect to the stators 434, which remain co-planar. In the rotatedstate, the conjugation of the molecule 430 is broken. Consequently, themolecule 430 is transparent (second spectral or optical state) andcomparatively less electrically conductive.

[0121] For the molecules of Example 2b, the films are constructed suchthat the molecular axis is parallel to the plane of the electrodes. Thismay involve films that are multiple monolayers thick. The molecules formsolid-state or liquid crystals in which the large stator groups arelocked into position by intermolecular interactions or direct bonding toa support structure, but the rotor is small enough to move within thelattice of the molecules. This type of structure can be used to build anE-field controlled display or used for other applications as mentionedearlier herein.

[0122] Model (2a): E-Field Induced Band Gap Change Caused by the Changeof Extended Conjugation Via Charge Separation or RecombinationAccompanied by Increasing or Decreasing Band Localization:

[0123]FIG. 6a is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via charge separation or recombination accompanied byincreasing or decreasing band localization. As shown in FIG. 6a, themolecule 630 comprises two portions 632 and 634. The molecule 630evidences a larger band gap state, with less π-delocalization.Application of an electric field causes charge separation in themolecule 630, resulting in a smaller band gap state, with betterπ-delocalization. Recombination of the charges returns the molecule 630to its original state.

[0124] The following requirements must be met in this model:

[0125] (a) The molecule must have a modest dielectric constant ε_(r) andcan be easily polarized by an external E-field, with ε_(r) in the rangeof 2 to 10 and polarization fields ranging from 0.01 to 10 V/nm;

[0126] (b) At least one segment of the molecule must have non-bondingelectrons, or π-electrons, or π-electrons and non-bonding electrons thatcan be mobilized over the entire molecule or a part of the molecule;

[0127] (c) The molecule can be symmetrical or asymmetrical;

[0128] (d) The inducible dipole(s) of the molecule can be oriented in atleast one direction;

[0129] (e) The charges will be separated either partially or completelyduring E-field induced polarization;

[0130] (f) The states of charge separation or recombination can beE-field de-pendent or bi-stable, stabilized through inter- orintra-molecular forces such as covalent bond formation, hydrogenbonding, charge attraction, Coulomb forces, metal complex, or Lewis acid(base) complex, etc.;

[0131] (g) The process of charge separation or recombination of themolecule can involve or not involve σ- and π-bond breakage or formation;and

[0132] (h) During the charge separation or re-combination processactivated by an E-field, the band gap of the molecule will changedepending on the degree of the non-bonding electron, or π-electron, orπ-electron and non-bonding electron de-localization in the molecule.Both optical and electrical properties of the molecules will be changedaccordingly.

[0133] One example of an E-field induced band gap change (color change)via charge separation or recombination involving bond breaking or bondformation is shown below (Example 3):

EXAMPLE 3

[0134] where:

[0135] The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups builtinto the molecule. The function of these tuning groups (e.g., OH, NHR,COOH, CN, nitro, etc.) is to provide an appropriate functional effect(e.g., both inductive effect and resonance effects) and/or stericeffects. The functional effect is to tune the band gap (ΔE_(HOMO /LUMO))of the molecule to get the desired electronic as well as opticalproper-ties of the molecule. The steric effect is to tune the moleculeconformation through steric hindrance, inter- or intra-molecularinteraction forces (e.g., hydrogen bonding, Coulomb interaction, van derWaals forces) to provide bi- or multiple-stability of molecularorientation. They may be any one of the following: hydrogen, hetero atom(e.g., N, O, S, P, B, F, Cl, Br and 1), functional group with at leastone of above-mentioned hetero atoms, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0136] The letter G₁ is a bridging group. The function of the bridginggroup is to connect two or more conjugated rings to achieve a desiredchromophore. The bridging group may be any one of the following: heteroatoms (e.g., N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH, etc.), hydrocarbon orsubstituted hydrocarbon.

[0137] The letter W is an electron-withdrawing group. The function ofthis group is to tune the reactivity of the maleic anhydride group ofthis molecule, which enables the molecule to undergo a smooth chargeseparation or recombination (bond breaking or formation, etc.) under theinfluence of an applied external E-field. The electron-withdrawing groupmay be any one of the following: carboxylic acid or its derivatives(e.g., ester or amide etc.), nitro, nitrile, ketone, aldehyde, sulfone,sulfuric acid or its derivatives, hetero atoms (e.g., F, Cl, etc.) orfunctional group with at least one of the hetero atoms (e.g., F, Cl, Br,N, O, S, etc.).

[0138] An example of an E-field induced band gap change involving theformation of a molecule-metal complex or a molecule-Lewis acid complexis shown below (Example 4):

EXAMPLE 4

[0139] where:

[0140] The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups builtinto the molecule. The function of these tuning groups (e.g., OH, NHR,COOH, CN, nitro, etc.) is to provide an appropriate functional effect(e.g. both inductive and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO /LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecular conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g., hydrogen bonding, Coulomb interaction, van der Waals forces) toprovide bi- or multiple-stability of the molecular orientation. They maybe any one of the following: hydrogen, hetero atom (e.g., N, O, S, P, B,F, Cl, Br, and I), functional group with at least one of theabove-mentioned hetero atoms, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0141] The letter G₁ is a bridging group. The function of the bridginggroup is to connect two or more conjugated rings to achieve a desiredchromophore. The bridging group may be any one of the following: heteroatoms (e.g., N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH, etc.) or substitutedhydrocarbon.

[0142] M⁺ represents metals, including transition metals, or theirhalogen complexes or H⁺ or other type of Lewis acid(s).

[0143] Model (2b): E-Field Induced Band Gap Change Caused by the Changeof Extended Conjugation via Charge Separation or Recombination andπ-Bond Breaking or Formation:

[0144]FIG. 6b is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via charge separation or recombination and π-bond breakingor formation. As shown in FIG. 6b, the molecule 630′ comprises twoportions 632′ and 634′. The molecule 630′ evidences a smaller band gapstate. Application of an electric field causes breaking of the π-bond inthe molecule 630′, resulting in a larger band gap state. Reversal of theE-field re-connects the π-bond between the two portions 632′ and 634′and returns the molecule 630′ to its original state.

[0145] The requirements that must be met in this model are the same aslisted for Model 2(a).

[0146] One example of an E-field induced band gap change cause byextended conjugation via charge separation (σ-bond breaking and π-bondformation) is shown below (Example 5):

EXAMPLE 5

[0147] where:

[0148] The letter Q is used here to designate a connecting unit betweentwo phenyl rings. It can be any one of following: S, O, NH, NR,hydrocarbon, or substituted hydrocarbon.

[0149] The letters Con₁ and Con₂ are connecting groups between onemolecule and another molecule or between a molecule and a solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (through a hydrogenbond), hetero atoms (i.e., N, O, S, P, etc.) or functional groups withat least one of above-mentioned hetero atoms (e.g., NH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

[0150] The letters R₁ and R₂ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbons (either saturated orunsaturated) or substituted hydrocarbons.

[0151] The letters J₁, J₂, J₃ and J₄ represent tuning groups built intothe molecule. The function of these tuning groups (e.g., OH, NHR, COOH,CN, nitro, etc.) is to provide an appropriate functional effect (e.g.both inductive and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO /LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecular conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g., hydrogen bonding, Coulomb interaction, van der Waals forces) toprovide bi- or multiple-stability of molecular orientation. They mayalso be used as spacing group to provide an appropriate 3-dimensionalscaffolding to allow the molecules to pack together while providingrotational space for each rotor. They may be any one of the following:hydrogen, hetero atom (e.g., N, O, S, P, B, F, Cl, Br, and I),functional group with at least one of above-mentioned hetero atom,hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

[0152] The letter G₁ is a bridging group. The function of the bridginggroup is to connect the stator and rotor or to connect two or moreconjugated rings to achieve a desired chromophore. The bridging groupmay be any one of the following: hetero atoms (e.g., N, O, S, P, etc.)or functional groups with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

[0153] The letter W is an electron-withdrawing group. The function ofthis group is to tune the reactivity of the lactone group of thismolecule, which enables the molecule to undergo a smooth chargeseparation or recombination (bond breaking or formation, etc.) under theinfluence of an applied external E-field. The electron-withdrawing groupmay be any one of the following: carboxylic acid or its derivatives(e.g., ester or amide etc.), nitro, nitrile, ketone, aldehyde, sulfone,sulfuric acid or its derivatives, hetero atoms (e.g., F, Cl, etc.) orfunctional group with at least one of hetero atoms (e.g., F, Cl, Br, N,O and S, etc.), hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

[0154] The uppermost molecular structure has a smaller band gap statethan the lowermost molecular structure.

[0155] Another example of an E-field induced band gap change caused bybreakage of extended π-bond conjugation via charge recombination andσ-bond formation is shown below (Example 6):

EXAMPLE 6

[0156] where:

[0157] The letter Q is used here to designate a connecting unit betweentwo phenyl rings. It can be any one of following: S, O, NH, NR,hydrocarbon, or substituted hydrocarbon.

[0158] The letters Con₁ and Con₂ are connecting groups between onemolecule and another molecule or between a molecule and a solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen, hetero atoms (i.e., N,O, S, P, etc.) or functional group with at least one of above-mentionedhetero atoms (e.g., NH, etc.), hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0159] The letters R₁ and R₂ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

[0160] The letters J₁, J₂, J₃ and J₄ represent tuning groups built intothe molecule. The function of these tuning groups (e.g., OH, NHR, COOH,CN, nitro, etc.) is to provide an appropriate functional effect (e.g.,both inductive and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO /LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecule conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g. hydrogen bonding, Coulomb interaction, van der Waals forces) toprovide bi- or multiple-stability of molecular orientation. They mayalso be used as spacing groups to provide an appropriate 3-dimensionalscaffolding to allow the molecules to pack together while providingrotational space for each rotor. They may be any one of the following:hydrogen, hetero atom (e.g., N, O, S, P, B, F, Cl, Br, and I),functional groups with at least one of above-mentioned hetero atom,hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

[0161] The letter G₁ is a bridging group. The function of this bridginggroup is to connect stator and rotor or to connect two or moreconjugated rings to achieve a desired chromophore. The bridging groupmay be any one of the following: hetero atoms (e.g., N, O, S, P, etc.)or functional group with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

[0162] The letter W is an electron-withdrawing group. The function ofthis group is to tune the reactivity of the lactone group of thismolecule, which enables the molecule to undergo a smooth chargeseparation or recombination (bond breaking or formation, etc.) under theinfluence of an applied external E-field. The electron-withdrawing groupmay be any one of the following: carboxylic acid or its derivatives(e.g., ester or amide, etc.), nitro, nitrile, ketone, aldehyde, sulfone,sulfuric acid or its derivatives, hetero atoms (e.g., F, Cl etc.) orfunctional group with at least one of hetero atoms (e.g., F, Cl, Br, N,O, S, etc.), hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

[0163] Again, the uppermost molecular structure has a smaller band gapstate than the lowermost molecular structure.

[0164] The present invention turns ink or dye molecules into activedevices that can be switched with an external electric field by amechanism completely different from any previously describedelectro-chromic or chromogenic material. The general idea is to usemodified Crystal Violet lactone type of molecules in which the C—O bondof the lactone is sufficiently labile enough and can undergo a bondbreaking and forming (see Examples 5 and 6 above) under the influence ofan applied electric field.

[0165] A positive and a negative charge are generated during the C—Obond breaking process. The resulting charges will be separated and movein opposite directions parallel to the applied external field (upperpart of the molecule), or bond rotation (lower part of the molecule. Thetwo aromatic rings with an extended dipole (upper part and lower part)of the molecule is completely conjugated, and a color (redshift) results(see Example 5). However, the molecule is designed to have inter- and/orintra-molecular forces, such as hydrogen bonding, Coulomb, ordipole-dipole interactions as well as steric repulsions, or by apermanent external E-field to stabilize both charges in this particularorientation. Thus, a large field is required to unlatch the moleculefrom its initial orientation. Once switched into a particularorientation, the molecule will remain in that orientation until it isswitched out.

[0166] When a reverse E-field is applied (Example 6), both charges tendto realign themselves to the direction of the reverse external field.The positive charge on the upper part of the molecule will migrate tothe center part of the molecule (tri-aryl methane position) from theside of the molecule through the non-bonding electron, or π-electron, orπ-electron and non-bonding electron delocalization. Likewise, thenegative charged lower part of the molecule will tend to move closer tothe external E-field through C—C bond rotation. A key component of themolecule design is that there is a steric and static repulsion betweenthe CO₂ ⁻ and the J₃ and J₄ groups that will prevent the lower part ofthe molecule (the negative charged sector) from rotating through acomplete 180 degree half cycle. Instead, the rotation is halted by thesteric interaction of bulky groups on the lower part and the upper partat an angle of approximately 90 degrees from the initial orientation.Furthermore, this 90 degree orientation is stabilized by a C—O bondformation and charge recombination. During this process, a tetrahedralcarbon (an isolator) is formed at the tri-aryl methane position. Theconjugation of the molecule is broken and the HOMO and LUMO are nolonger delocalized over the entire upper part of the molecule. This hasthe effect of shrinking the size of the volume occupied by theelectrons, which causes the HOMO-LUMO gap to increase. A blue-shiftedcolor or transparent state will result during this process.

[0167] For colored ink and dye molecules, the limitation of the positivecharge migration just between one side of a molecule and the centerposition is crucial. Another important factor is the ability to switchthe rotor (lower part of molecule) between two states separated by anoptically significant angle (nominally 10 to 170 degrees) from thestators (the upper part of the molecule). When the intra-molecularcharge separation reaches a maximum distance, then the upper most partof the molecule becomes completely conjugated. Thus, the π-electrons orπ-electrons and nonbonding electrons of the molecule, through itshighest occupied molecular orbital (HOMO) and lowest unoccupiedmolecular orbital (LUMO), are delocalized over the upper most region.The effect is identical to that for a quantum mechanical particle in abox: when the box is the size of the entire molecule, i.e., when theorbitals are delocalized, then the gap between the HOMO and LUMO isrelatively small. In this case, the HOMO-LUMO gap of the molecule isdesigned to yield the desired color of the ink or dye. The HOMO-LUMO gapfor the all-parallel structure can be tuned by substituting variouschemical groups (J₁, J₂, J₃, J₄, and W) onto the different aromaticrings of the molecule. In the case where the rotor (lower part of themolecule) is rotated by 10 to 170 degrees with respect to the stators(the upper part of the molecule), depending on the nature of thechemical substituents (J₁, J₂, J₃, J₄, and W) bonded to the rotor andstator, then the increased HOMO-LUMO gap will correspond to a color thatis blue-shifted with respect to the color of the all-parallel structure.With sufficient shifting, the molecule becomes transparent, if the newHOMO-LUMO gap is large enough. Thus, the molecule is switchable betweentwo colors or from one color to a transparent state.

[0168] Examples 5 and 6 show two different states of a representativeswitchable molecule under the influence of an externally appliedE-field. For this particular type of molecule, a sufficiently thickmolecular film is grown, for example using Langmuir-Blodgett techniques,vapor phase deposition, or electrochemical deposition, such that theorientation axis of the molecules is perpendicular to the plane of theelectrodes used to switch the molecules. Another deposition technique isto suspend the molecule as a monomer/oligomer or solvent-based solutionthat is thick film coated (e.g., reverse roll) or spin-coated onto thesubstrate and subsequently polymerized (e.g., by UV radiation) or driedwhile the coating is subjected to an electric field that orients themolecule. A top electrode may be a transparent conductor, such asindium-tin oxide, and the films are grown such that the molecular axisis parallel to the plane of the electrodes. The molecules formsolid-state or liquid crystals in which the large stator groups arelocked into position by intermolecular interactions or direct bonding toa support structure, but the rotor is small enough to move within thelattice of the molecules.

[0169] Model (3): E-Field Induced Band Gap Change via Molecular Foldingor Stretching

[0170]FIG. 7 is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via molecular folding or stretching. As shown in FIG. 7, themolecule 730 comprises three portions 732, 734, and 736. The molecule730 evidences a smaller band gap state due to an extended conjugationthrough a large region of the molecule. Application of an electric fieldcauses breaking of the conjugation in the molecule 730, due to molecularfolding about the central portion 734, resulting in a larger band gapstate due to the non-extended conjugation in the large region of themolecule. Reversal of the E-field unfolds the molecule 730 and returnsthe molecule to its original state. Stretching and relaxing of thecentral portion 734 of the molecule 730 has the same effect.

[0171] The following requirements must be met in this Model:

[0172] (a) The molecule must have at least two segments;

[0173] (b) Several segments (portions) should have non-bondingelectrons, or π-electrons, or π-electrons and non-bonding electronsinvolved in the HOMOs, LUMOs, and nearby orbitals;

[0174] (c) The molecule may be either symmetrical or asymmetrical with adonor group on one side and an acceptor group on another side;

[0175] (d) At least two segments of the molecule have some functionalgroups that will help to stabilize both states of folding and stretchingthrough intra- or intermolecular forces such as hydrogen bonding, vander Waals forces, Coulomb attraction or metal complex formation;

[0176] (e) The folding or stretching states of the molecule must beE-field addressable;

[0177] (f) In at least one state (presumably in a fully stretchedstate), the nonbonding electrons, or π-electrons, or π-electrons andnon-bonding electrons of the molecule will be well-delocalized, and theπ- and p-electrons electrons of the molecule will be localized or onlypartially delocalized in other state(s);

[0178] (g) The band gap of the molecules will change depending on thedegree of non-bonding electron, or π-electron, or π-electron andnon-bonding electron delocalization while the molecule is folded orstretched by an applied external E-field, and this type of change willalso affect the electrical or optical properties of the molecule aswell; and

[0179] (h) This characteristic can be applied to these types ofmolecules for optical or electrical switches, gates, storage or displayapplications.

[0180] An example of an E-field induced band gap change via molecularfolding or stretching is shown below (Example 7):

EXAMPLE 7

[0181] where:

[0182] The letters R₁ and R₂ represent spacing groups built into themolecule. They may be any one of the following: hydrogen, hydrocarbon(either saturated or unsaturated) or substituted hydrocarbon.

[0183] The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups builtinto the molecule. The function of these tuning groups (e.g., OH, NHR,COOH, CN, nitro, etc.) is used to provide an appropriate functionaleffect (e.g., both inductive and resonance effects) and/or stericeffects. The functional effect is to tune the band gap (ΔE_(HOMO /LUMO))of the molecule to get the desired electronic as well as opticalproperties of the molecule. The steric effect is to tune the molecularconformation through steric hindrance, inter- or intra-molecularinteraction forces (e.g. hydrogen bonding, Coulomb interaction, van derWaals forces) to provide bi- or multiple-stability of molecularorientation. They may also be used as spacing group They may be any oneof the following: hydrogen, hetero atom (e.g., N, O, S, P, B, F, Cl, Brand I), functional group with at least one of above-mentioned heteroatom, hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

[0184] Letters Y and Z are functional groups that will form inter- orintramolecular hydrogen bonding. They may be any one of following: SH,OH, amine, hydrocarbon, or substituted hydrocarbon.

[0185] The molecule on the top of the graphic has a larger band gap dueto the localized conjugation various parts of the molecule, while themolecule on the bottom has a smaller band gap due to an extendedconjugation through a large region of the molecule.

[0186] The technology disclosed and claimed herein for forming opticalswitches (micro-meter or nanometer) may be used to assemble displays,electronic books, rewrittable media, electrically tunable opticallenses, electrically controlled tinting for windows and mirrors, opticalcrossbar switches for routing signals from one of many incoming channelsto one of many outgoing channels, and more.

INDUSTRIAL APPLICABILITY

[0187] The field-switchable molecules disclosed herein are expected tofind use in optical devices constructed from micro-scale and evennano-scale components as well as a variety of visual displays.

What is claimed is:
 1. An electric field activated optical switch comprising a molecular system configured within an electric field generated by a pair of electrodes, said molecular system having an electric field induced band gap change that occurs via one of the following mechanisms: (1) molecular conformation change or an isomerization; (2) change of extended conjugation via chemical bonding change to change the band gap; or (3) molecular folding or stretching.
 2. The optical switch of claim 1 wherein said electric field induced band gap change occurs via molecular conformation change or an isomerization.
 3. The optical switch of claim 2 wherein said molecular system comprises at least one stator portion and at least one rotor portion, wherein said rotor rotates from a first state to a second state with an applied electric field, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively smaller band gap, and wherein in said second state, said extended conjugation is destroyed, resulting in a relatively larger band gap.
 4. The optical switch of claim 3 wherein said molecular system comprises

where: A⁻ is an Acceptor group comprising an electron-withdrawing group selected from the group consisting of: (a) hydrogen, (b) carboxylic acid and its derivatives, (c) sulfuric acid and its derivatives, (d) phosphoric acid and its derivatives, (e) nitro, (f) nitrile, (g) hetero atoms selected from the group consisting of N, O, S, P, F, Cl, and Br, (h) functional groups with at least one of said hetero atoms, (i) saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons; D⁺ is a Donor group comprising an electron-donating group selected from the group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e) ethers, (f) saturated or unsaturated hydrocarbon, (g) substituted hydrocarbons, and (h) functional groups with at least one hetero atom selected from the group consisting of B, Si, I, N, O, S, and P, wherein said Donor group is more electropositive than said Acceptor group; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and SA and SB designate Stator A and Stator B, respectively, which may be the same or different and which are independently selected from the group consisting of (a) unsaturated or saturated hydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbon units contain conjugated rings that contribute to an extended conjugation of the molecule when it is in a planar state (red shifted state), wherein said stators optionally and separately contain at least one bridging group G_(n), at least one spacing group R_(n), or both, wherein said at least one bridging group is either (a) selected from the group consisting of acetylene, ethylene, amide, imide, imine, and azo and is used to connect said stators to said rotor or to connect at least two conjugated rings to achieve a desired chromophore or (b) selected from the group consisting of a single atom bridge and a direct sigma bond between said rotor and said stators and wherein said at least one spacing group is selected from the group consisting of phenyl, isopropyl, and tert-butyl and is used to provide an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor to rotate over a desired range of motion.
 5. The optical switch of claim 4 wherein said molecular system comprises

where: A⁻ is said Acceptor group; D⁺ is said Donor group; Con₁ and Con₂ are said connecting units; R₁, R₂, R₃ are said spacing groups, which are independently selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; and G₁, G₂, G₃, and G₄ are said bridging groups, which are independently selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons.
 6. The optical switch of claim 3 wherein said molecular system comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing group selected from the group consisting of: (a) hydrogen, (b) carboxylic acid and its derivatives, (c) sulfuric acid and its derivatives, (d) phosphoric acid and its derivatives, (e) nitro, (f) nitrile, (g) hetero atoms selected from the group consisting of N, O, S, P, F, Cl, and Br, (h) functional groups with at least one of said hetero atoms, (i) saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons; D⁺ is a Donor group comprising an electron-donating group selected from the group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e) ethers, (f) saturated or unsaturated hydrocarbon, (g) substituted hydrocarbons, and (h) functional groups with at least one hetero atom selected from the group consisting of B, Si, I, N, O, S, and P, wherein said Donor group is more electropositive than said Acceptor group; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and SA and SB designate Stator A and Stator B, respectively, which may be the same or different and which are independently selected from the group consisting of (a) unsaturated or saturated hydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbon units contain conjugated rings that contribute to an extended conjugation of the molecule when it is in a planar state (red shifted state), wherein said stators optionally and separately contain at least one bridging group G_(n), at least one spacing group R_(n), or both, wherein said at least one bridging group is either (a) selected from the group consisting of acetylene, ethylene, amide, imide, imine, and azo and is used to connect said stators to said rotor or to connect at least two conjugated rings to achieve a desired chromophore or (b) selected from the group consisting of a single atom bridge and a direct sigma bond between said rotor and said stators and wherein said at least one spacing group is selected from the group consisting of phenyl, isopropyl, and tert-butyl and is used to provide an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor to rotate over a desired range of motion.
 7. The optical switch of claim 6 wherein said molecular system comprises:

where: A⁻ is said Acceptor group; D⁺ is said Donor group; Con₁ and Con₂ are said connecting units; R₁, R₂ and R₃ are said spacing groups, which are independently selected from the group consisting of (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; G₁, G₂, G₃, G₄, G₅, G₆, G₇, and G₈ are said bridging groups, which are independently selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and J₁ and J₂ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons.
 8. The optical switch of claim 1 wherein said electric field induced band gap occurs via a change of extended conjugation via chemical bonding change to change the band gap.
 9. The optical switch of claim 8 wherein said electric field induced band gap change occurs via a change of extended conjugation via charge separation or recombination accompanied by increasing or decreasing band localization.
 10. The optical switch of claim 9 wherein said molecular system comprises two portions, wherein a change from a first state to a second state occurs with an applied electric field, said change involving charge separation in changing from said first state to said second state, thereby resulting in a relatively larger band gap state, with less π-delocalization, and recombination of charge in changing from said second state to said first state, thereby resulting in a relatively smaller band gap state, with greater π-delocalization.
 11. The optical switch of claim 10 wherein said molecular system comprises:

where: J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 12. The optical switch of claim 10 wherein said molecular system comprises:

where: J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and M⁺ is selected from the group consisting of transition metals, their halogen complexes, H⁺, and Lewis acids.
 13. The optical switch of claim 8 wherein said electric field induced band gap occurs via a change of extended conjugation via charge separation or recombination and π-bond breaking or formation.
 14. The optical switch of claim 13 wherein said molecular system comprises two portions, wherein a change from a first state to a second state occurs with an applied electric field, said change involving charge separation in changing from said first state to said second state, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively larger band gap state, and wherein in said second state, said extended conjugation is destroyed and separated positive and negative charges are created within said molecular system, resulting in a relatively smaller band gap state.
 15. The optical switch of claim 14 wherein said molecular system comprises:

where: Q is a connecting unit between two phenyl rings and is selected from the group consisting of: S, O, NH, NR, hydrocarbon, or substituted hydrocarbon; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; R₁ and R₂ are spacing groups for providing an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor, said spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbon, and (c) substituted hydrocarbon; J₁, J₂, J₃, and J₄ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect either (a) a stator portion and a rotor portion of said molecular system or (b) at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 16. The optical switch of claim 14 wherein said molecular system comprises:

where: Q is a connecting unit between two phenyl rings and is selected from the group consisting of: S, O, NH, NR, hydrocarbon, or substituted hydrocarbon; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; R₁ and R₂ are spacing groups for providing an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor, said spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbon, and (c) substituted hydrocarbon; J₁, J₂, J₃, and J₄ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect either (a) a stator portion and a rotor portion of said molecular system or (b) at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 17. The optical switch of claim 1 wherein said electric field induced band gap change occurs via molecular folding or stretching.
 18. The optical switch of claim 17 wherein said molecular system comprises three portions, a first portion and a third portion, each bonded to a second, central portion, wherein a change from a first state to a second state occurs with an applied electric field, said change involving a folding or stretching about or of said second portion, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively smaller band gap state, and wherein in said second state, said extended conjugation is destroyed, resulting in a relatively larger band gap.
 19. The optical switch of claim 18 wherein said molecular system comprises:

where: R₁ and R₂ are spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and Y and Z are functional groups that form inter-molecular or intra-molecular hydrogen bonding and are selected from the group consisting of: (a) SH, (b) OH, (c) amine, (d) hydrocarbons, and (e) substituted hydrocarbons.
 20. The optical switch of claim 1 wherein said molecular system is bi-stable, which provides a non-volatile component.
 21. The optical switch of claim 1 wherein said molecular system has essentially a low activation barrier between different states to provide a fast, but volatile, switch.
 22. The optical switch of claim 1 wherein said molecular system has more than two switchable states, such that optical properties of said molecular system can be tuned by either continuously by application of a decreasing or increasing electric field to form a volatile switch or the color is changed abruptly by the application of voltage pulses to a switch with at least one activation barrier.
 23. The optical switch of claim 1 wherein said molecular system changes between a transparent state and a colored state.
 24. The optical switch of claim 1 wherein said molecular system changes between one colored state and another colored state.
 25. The optical switch of claim 1 wherein said molecular system changes between one index of refraction and another index of refraction.
 26. A molecular system capable of undergoing an electric field induced band gap change that occurs via one of the following mechanisms: (1) molecular conformation change or an isomerization; (2) change of extended conjugation via chemical bonding change to change the band gap; or (3) molecular folding or stretching.
 27. The molecular system of claim 26 wherein said electric field induced band gap change occurs via molecular conformation change or an isomerization.
 28. The molecular system of claim 27 comprising at least one stator portion and at least one rotor portion, wherein said rotor rotates from a first state to a second state with an applied electric field, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively smaller band gap, and wherein in said second state, said extended conjugation is destroyed, resulting in a relatively larger band gap.
 29. The molecular system of claim 28 comprising:

where: A⁻ is an Acceptor group comprising an electron-withdrawing group selected from the group consisting of: (a) hydrogen, (b) carboxylic acid and its derivatives, (c) sulfuric acid and its derivatives, (d) phosphoric acid and its derivatives, (e) nitro, (f) nitrile, (g) hetero atoms selected from the group consisting of N, O, S, P, F, Cl, and Br, (h) functional groups with at least one of said hetero atoms, (i) saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons; D⁺ is a Donor group comprising an electron-donating group selected from the group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e) ethers, (f) saturated or unsaturated hydrocarbon, (g) substituted hydrocarbons, and (h) functional groups with at least one hetero atom selected from the group consisting of B, Si, I, N, O, S, and P, wherein said Donor group is more electropositive than said Acceptor group; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and SA and SB designate Stator A and Stator B, respectively, which may be the same or different and which are independently selected from the group consisting of (a) unsaturated or saturated hydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbon units contain conjugated rings that contribute to an extended conjugation of the molecule when it is in a planar state (red shifted state), wherein said stators optionally and separately contain at least one bridging group G_(n), at least one spacing group R_(n), or both, wherein said at least one bridging group is either (a) selected from the group consisting of acetylene, ethylene, amide, imide, imine, and azo and is used to connect said stators to said rotor or to connect at least two conjugated rings to achieve a desired chromophore or (b) selected from the group consisting of a single atom bridge and a direct sigma bond between said rotor and said stators and wherein said at least one spacing group is selected from the group consisting of phenyl, isopropyl, and tert-butyl and is used to provide an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor to rotate over a desired range of motion.
 30. The molecular system of claim 29 comprising:

where: A⁻ is said Acceptor group; D⁺ is said Donor group; Con₁ and Con₂ are said connecting units; R₁, R₂, R₃ are said spacing groups, which are independently selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; and G₁, G₂, G₃, and G₄ are said bridging groups, which are independently selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons.
 31. The molecular system of claim 28 comprising:

where: A⁻ is an Acceptor group comprising an electron-withdrawing group selected from the group consisting of: (a) hydrogen, (b) carboxylic acid and its derivatives, (c) sulfuric acid and its derivatives, (d) phosphoric acid and its derivatives, (e) nitro, (f) nitrile, (g) hetero atoms selected from the group consisting of N, O, S, P, F, Cl, and Br, (h) functional groups with at least one of said hetero atoms, (i) saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons; D⁺ is a Donor group comprising an electron-donating group selected from the group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e) ethers, (f) saturated or unsaturated hydrocarbon, (g) substituted hydrocarbons, and (h) functional groups with at least one hetero atom selected from the group consisting of B, Si, I, N, O, S, and P, wherein said Donor group is more electropositive than said Acceptor group; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and SA and SB designate Stator A and Stator B, respectively, which may be the same or different and which are independently selected from the group consisting of (a) unsaturated or saturated hydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbon units contain conjugated rings that contribute to an extended conjugation of the molecule when it is in a planar state (red shifted state), wherein said stators optionally and separately contain at least one bridging group G_(n), at least one spacing group R_(n), or both, wherein said at least one bridging group is either (a) selected from the group consisting of acetylene, ethylene, amide, imide, imine, and azo and is used to connect said stators to said rotor or to connect at least two conjugated rings to achieve a desired chromophore or (b) selected from the group consisting of a single atom bridge and a direct sigma bond between said rotor and said stators and wherein said at least one spacing group is selected from the group consisting of phenyl, isopropyl, and tert-butyl and is used to provide an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor to rotate over a desired range of motion.
 32. The molecular system of claim 31 comprising:

where: A⁻ is said Acceptor group; D⁺ is said Donor group; Con₁ and Con₂ are said connecting units; R₁, R₂ and R₃ are said spacing groups, which are independently selected from the group consisting of (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; G₁, G₂, G₃, G₄, G₅, G₆, G₇, and G₈ are said bridging groups, which are independently selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and J₁ and J₂ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons.
 33. The molecular system of claim 26 wherein said electric field induced band gap occurs via a change of extended conjugation via chemical bonding change to change the band gap.
 34. The molecular system of claim 33 wherein said electric field induced band gap change occurs via a change of extended conjugation via charge separation or recombination accompanied by increasing or decreasing band localization.
 35. The molecular system of claim 34 comprising two portions, wherein a change from a first state to a second state occurs with an applied electric field, said change involving charge separation in changing from said first state to said second state, thereby resulting in a relatively larger band gap state, with less π-delocalization, and recombination of charge in changing from said second state to said first state, thereby resulting in a relatively smaller band gap state, with greater π-delocalization.
 36. The molecular system of claim 35 comprising:

where: J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 37. The molecular system of claim 35 comprising:

where: J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and M⁺ is selected from the group consisting of transition metals, their halogen complexes, H⁺, and Lewis acids.
 38. The molecular system of claim 33 wherein said electric field induced band gap occurs via a change of extended conjugation via charge separation or recombination and π-bond breaking or formation.
 39. The molecular system of claim 38 wherein said molecular system comprises two portions, wherein a change from a first state to a second state occurs with an applied electric field, said change involving charge separation in changing from said first state to said second state, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively larger band gap state, and wherein in said second state, said extended conjugation is destroyed and separated positive and negative charges are created within said molecular system, resulting in a relatively smaller band gap state.
 40. The molecular system of claim 39 comprising:

where: Q is a connecting unit between two phenyl rings and is selected from the group consisting of: S, O, NH, NR, hydrocarbon, or substituted hydrocarbon; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; R₁ and R₂ are spacing groups for providing an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor, said spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbon, and (c) substituted hydrocarbon; J₁, J₂, J₃, and J₄ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect either (a) a stator portion and a rotor portion of said molecular system or (b) at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 41. The molecular system of claim 39 wherein said molecular system comprises:

where: Q is a connecting unit between two phenyl rings and is selected from the group consisting of: S, O, NH, NR, hydrocarbon, or substituted hydrocarbon; Con₁ and Con₂ are connecting units between one molecule and another molecule or between a molecule and a solid substrate selected from the group consisting of a metal electrode, an inorganic substrate, and an organic substrate, said connecting units independently selected from the group consisting of: (a) hydrogen (utilizing a hydrogen bond), (b) multivalent hetero atoms selected from the group consisting of C, N, O, S, and P, (c) functional groups containing said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; R₁ and R₂ are spacing groups for providing an appropriate 3-dimensional scaffolding to allow molecules to pack together while providing rotational space for each rotor, said spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbon, and (c) substituted hydrocarbon; J₁, J₂, J₃, and J₄ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; G₁ is a bridging group to connect either (a) a stator portion and a rotor portion of said molecular system or (b) at least two conjugated rings to achieve a desired chromophore, said bridging group selected from the group consisting of: (a) hetero atoms selected from the group consisting of N, O, S, and P, (b) functional groups with at least one of said hetero atoms, (c) saturated or unsaturated hydrocarbons, and (d) substituted hydrocarbons; and W is an electron-withdrawing group for tuning reactivity of the maleic anhydride group of said molecular system, which enables said molecular system to undergo a smooth charge separation or recombination upon application of said electric field, said electron-withdrawing group selected from the group consisting of: (a) carboxylic acid and its derivatives, (b) nitro, (c) nitrile, (d) ketone, (e) aldehyde, (f) sulfone, (g) sulfuric acid and its derivatives, (h) hetero atoms selected from the group consisting of F, Cl, Br, N, O and S, and (i) functional groups with at least one of said hetero atoms.
 42. The molecular system of claim 26 wherein said electric field induced band gap change occurs via molecular folding or stretching.
 43. The molecular system of claim 42 wherein said molecular system comprises three portions, a first portion and a third portion, each bonded to a second, central portion, wherein a change from a first state to a second state occurs with an applied electric field, said change involving a folding or stretching about or of said second portion, wherein in said first state, there is extended conjugation throughout said molecular system, resulting in a relatively smaller band gap state, and wherein in said second state, said extended conjugation is destroyed, resulting in a relatively larger band gap.
 44. The molecular system of claim 43 wherein said molecular system comprises:

where: R₁ and R₂ are spacing groups selected from the group consisting of: (a) hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substituted hydrocarbons; J₁, J₂, J₃, J₄ and J₅ are tuning groups to provide at least one appropriate functional effect selected from the group consisting of inductive effects, resonance effects, and steric effects, said tuning groups being selected from the group consisting of: (a) hydrogen, (b) hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl, Br and I, (c) functional groups with at least one of said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e) substituted hydrocarbons; and Y and Z are functional groups that form inter-molecular or intra-molecular hydrogen bonding and are selected from the group consisting of: (a) SH, (b) OH, (c) amine, (d) hydrocarbons, and (e) substituted hydrocarbons. 